The toad urinary bladder, a widely used model for the human renal tubule, has the same salt and water conservation functions, and responds to the same regulation hormones (aldosterone and antidiuretic hormone) and drugs which affecthuman salt and water metabolism. Aldosterone is thought to stimulate sodium transport by inducing new protein synthesis; antidiuretic hormone (ADH) is thought to stimulate both sodium and water transport by an intermediate, cyclic adenosine-3', 5' -monophosphate (cAMP). However, neither a specific aldosterone-induced protein (AIP), or a rapidly-responsive, ADH- or cAMP-sensitive membrane component has been demonstrated. Active sodium transport is thought to be regulated by an "electrogenic" sodium pump; but an alternative "fixed-charge" hypothesis, based on our previous data, suggests that such physiological properties can arise from an asymmetrical, ion-selective, fixed-charge membrane, which is regulated by specific hormones. This project combines electrophysiological and biochemical investigations of salt and water transport across the toad bladder. The proposed AIP, demonstrated in our preliminary experiments, will be isolated and characterized; the ADH- and/or cAMP-sensitive molecules will be sought by similar means. Hypotheses will be tested by physico-chemical techniques designed to clarify the basis for hromone and drug action. Measurements will include: electrical potential differences; short-circuit current; transepithelial resistance; osmotic water flow; isotope flux; radiotracer incorporation into proteins and nucleic acids; gradient slab gel and high voltage electrophoresis; chromatography; autoradiography; and tissue culture. Physico-chemical variables will include: ion and non-electrolyte composition, enzymes, drugs, pH and osmotic pressure. Ion selectivity sequences will be established for each isolated molecule. The fixed-charge model for renal ion transport which will be developed may be applicable to many cellular control mechanisms. These studies will be stimulate clinical research in fluid and electrolyte disorders, such as those associated with cardiac and renal disease, and will develop agents for their treatment.